How do I bottom-align grid elements in bootstrap fluid layout

I have a fluid layout using Twitter's bootstrap, wherein I have a row with two columns. The first column has a lot of content, which I want to fill the span normally. The second column just has a button and some text, which I want to bottom align relative to the cell in the first column.

Here's what I have:

-row-fluid-------------------------------------
+-span6----------+ +-span6----------+
|                | |short content   |
| content        | +----------------+
| that           | 
| is tall        |    
|                |
+----------------+
-----------------------------------------------

Here's what I want:

-row-fluid-------------------------------------
+-span6----------+
|                |
| content        |
| that           | 
| is tall        | +-span6----------+    
|                | |short content   |
+----------------+ +----------------+
-----------------------------------------------

I've seen solutions that make the first span an absolute height, and position the second span relative to it, but a solution where I didn't have to specify the absolute height of my divs would be preferred. I'm also open to a complete rethink of how to achieve the same effect. I'm not married to this use of the scaffolding, it just seemed to make the most sense to me.

This layout as a fiddle:

http://jsfiddle.net/ryansturmer/A7buv/3/

This is an updated solution for Bootstrap 3 (should work for older versions though) that uses CSS/LESS only:

http://jsfiddle.net/silb3r/0srp42pb/11/

You set the font-size to 0 on the row (otherwise you'll end up with a pesky space between columns), then remove the column floats, set display to inline-block, re-set their font-size, and then vertical-align can be set to anything you need.

No jQuery required.

Please note: for Bootstrap 4+ users, please consider Christophe's solution (Bootstrap 4 introduced flexbox, which provides for a more elegant CSS-only solution). The following will work for earlier versions of Bootstrap...

See http://jsfiddle.net/jhfrench/bAHfj/ for a working solution.

//for each element that is classed as 'pull-down', set its margin-top to the difference between its own height and the height of its parent
$('.pull-down').each(function() {
  var $this = $(this);
  $this.css('margin-top', $this.parent().height() - $this.height())
});

On the plus side:

• in the spirit of Bootstrap's existing helper classes, I named the class pull-down.
• only the element that is getting "pulled down" needs to be classed, so...
• ...it's reusable for different element types (div, span, section, p, etc)
• it's fairly-well supported (all the major browsers support margin-top)

Now the bad news:

• it requires jQuery
• it's not, as-written, responsive (sorry)

You can use flex:

@media (min-width: 768px) {
  .row-fluid {
    display: flex;
    align-items: flex-end;
  }
}